The next year of this grant we propose to extend our studies of tau protein. We expect to purify from chick brain and other sources to study its phylogenetic divergence. Peptide mapping and partial sequence analysis will be used. We will attempt to find the source of the microheterogeneity seen in tau protein from a variety of sources. Further studies are planned of the mechanism of microtubule regulation in the Xenopus egg oocyte system and the nucleation of microtubule growth off the kinetochore region of metaphase chromosomes.